AIR CONDITIONER WITH AN OPERATION CONTROL DEVICE

Abstract: A receiver (4) is provided on a main line (9a) and a bypass path (4a) provided with an on-off valve (SV) is formed for allowing gas refrigerant inside the receiver (4) to flow into a low-pressure liquid line. In addition, a defrosting operation is effected with a motorized expansion valve (5) fully closed and the on-off valve (SV) open. At the beginning of the defrosting operation, the on-off valve (SV) is put in a closed state and it is also put in the closed state when the discharge pipe temperature Td becomes equal to or lower than a predetermined temperature. In addition, when the discharge pipe temperature Td becomes equal to or higher than the predetermined temperature, the motorized expansion valve (5) temporarily opens to a predetermined valve travel, and when the defrosting operation is completed, the on-off valve (SV) is opened in a heating cycle and the motorized expansion valve (5) is gradually opened.

Description: This invention relates to an air conditioner of the kind as referred to in the preamble of claim 1, in particular with respect to controlling the air conditioner during and just after completion of a defrosting operation. In a conventional air conditioner as disclosed in Japanese Patent Application Laid-Open Gazette No.4-344085, an indoor unit is connected to an outdoor unit in which a compressor, a four-way selector valve, a thermal-source-side heat exchanger, a motor-operated expansion valve and a receiver are sequentially connected. The air conditioner performs defrosting operation when a fin of the thermal-source-side heat exchanger is frosted in heating operation. A defrosting operation is executed in a cooling cycle whereby a motor-operated expansion valve of the indoor unit and a motor-operated expansion valve of the outdoor unit are both fully opened. The known air conditioner is further provided with an accumulator on the suction side of the compressor for preventing operation in a wet condition of the compressor. The motor-operated expansion valves are fully opened in the defrosting operation which results in a decreased operation performance of the air conditioner due to pressure loss at the accumulator. If the accumulator were not provided and the defrosting operation would as well be executed with the fully opened expansion valves, then liquid refrigerant condensed by the thermal-source-side heat exchanger would be stored in the receiver in the case of heavy frost, low open-air temperature or short refrigerant piping. Therefore sufficient heat required for defrosting would be missing and liquid refrigerant in the receiver would flow back to the compressor. This would promote operation of the refrigerant circuit in a wet condition of the compressor so that the compressor would come under stress. The reliability of the compressor would then be reduced. The present invention is to overcome the above described problems and it is an object of this invention to enhance operation performance without the use of an accumulator while avoiding that the compressor will operate in a wet condition during defrosting operation. According to the present invention, this object is achieved by an air conditioner as defined in claim 1. During a defrosting operation, gas refrigerant from a receiver is introduced into a main line of the refrigerant circuit via a bypass passage which bypasses the expansion mechanism. The air conditioner of the invention comprises a refrigerant circuit which has a main line in which a compressor, a thermal-source-side heat exchanger, an expansion mechanism freely adjustable in opening and a used-side heat exchanger are sequentially connected. The refrigerant circuit is reversibly operable between a cooling cycle operation and a heating cycle operation by means of an operation control device. The air conditioner further comprises a receiver which is provided in a high-pressure liquid line of the main line of the refrigerant circuit. There is further provided a bypass passage which is connected at one end thereof to the receiver and at the other end to a low-pressure liquid line of the main line of the refrigerant circuit downstream of the expansion mechanism for bypassing the expansion mechanism and for introducing gas refrigerant from the receiver into the low-pressure liquid line. The bypass passage is provided with open/shut-off means for opening and shutting off the bypass passage. There are further provided defrosting executing means for fully closing the expansion mechanism and opening the open/shut-off means in response to a defrosting requiring signal in the heating cycle operation of the refrigerant circuit and for executing defrosting in its cooling cycle operation. Preferably, the air conditioner of the invention comprises initial control means for outputting an initially closing signal to the defrosting executing means so that the open/-shut-off means is closed until a set time has passed after the start of the defrosting operation. Advantageously, the air conditioner comprises wet condition control means for outputting a closing signal to the defrosting executing means so that the open/shut-off means is closed when refrigerant temperature on the discharge side of the compressor drops to or below a specified temperature. In this connection a specific measure comprises the output of an opening holding signal by such a wet condition control means for holding the open/shut-off means opened for a set time after it has been closed for a set time. Preferably, the air conditioner of the invention comprises superheating control means for outputting opening and closing signals to the defrosting executing means so that when refrigerant temperature on the discharge side of the compressor rises to or above a specified temperature the expansion mechanism is first opened to a specified opening state and then fully closed. In this connection a specific measure comprises the output of a closing holding signal to the defrosting executing means for holding the expansion mechanism fully closed for a set time after it has first been opened. Advantageously, the air conditioner comprises operation shifting means for shifting a circuit to the heating cycle operation when the defrosting executing means has completed defrosting or holding the open/shut-off means open for a set time and then closing it while gradually opening the expansion mechanism to a specified opening state. With the above structure the defrosting executing means will accordingly start defrosting operation in the cooling cycle operation of the refrigerant circuit in response to a defrosting requiring signal. The open/shut-off means will in this case be opened while the expansion mechanism will be fully closed. At an initial stage of the defrosting operation the open/shut-off means will be closed however. Both the main line and the bypass passage will therefore be shut off for preventing reverse flow of the liquid refrigerant from the refrigerator. When refrigerant temperature on the discharge side of the compressor drops to or below a specified temperature, the open/shut-off means is closed. Being closed for a set time this will prevent an excessive opening/closing operation of the open/shut-off means and also of the expansion mechanism and will therefore avoid operation of the compressor in a superheated condition. In the case where refrigerant temperature on the discharge side of the compressor rises to or above a specified temperature the expansion mechanism will be opened. Liquid refrigerant in the receiver will then flow back to thereby prevent operation of the compressor in the superheated condition. The expansion mechanism will subsequently be held in the fully closed state for a set time which again prevents excessive opening/closing operation of the expansion mechanism. Since during defrosting operation gas refrigerant from the receiver is introduced into the main line through a bypass passage, liquid refrigerant when condensed in the thermal-source-side heat exhanger and stored in the receiver in the case of heavy frost, low open-air temperature or short refrigerant piping can be securely prevented from flowing back to the compressor even without the provision of an accumulator. Any operation of the compressor in a wet condition can therefore be securely prevented so that the compressor will not be subjected to stress and its reliability will thereby be enhanced. Since no accumulator is needed, pressure loss can be decreased which enhances operation performance and reduces at the same time the number of elements resulting accordingly in a reduction of costs. When both the main line and the bypass passage are shut off at the initial stage of the defrosting operation as provided under a preferred embodiment of the invention, it then can be securely prevented that liquid refrigerant in the receiver flows into the thermal-source-side heat exchanger and the used-side heat exchanger due to variation in pressure of the refrigerant circuit. Thus, reverse flow of liquid refrigerant to the compressor can be prevented and a condensation area in the thermal-source-side heat exchanger can be sufficiently ensured, so that defrosting performance can be increased. When both the main line and the bypass passage are shut off at the time when refrigerant temperature on the discharge side of the compressor drops in the defrosting operation, then liquid refrigerant on the suction side of the compressor can be evaporated. Consequently, reverse flow of liquid refrigerant can also be prevented so that operation in wet condition of the compressor can be securely prevented, thereby further enhancing reliability of the compressor. When communication with the bypass passage is held for a set time after both the main line and the bypass passage are shut off, the compressor can then be prevented in advance from operation in superheated condition due to frequent shutting-off control of the refrigerant circuit. When refrigerant temperature on the discharge side of the compressor rises in the defrosting operation, the expansion mechanism will be opened and communication will be established in the main line. Thus, liquid refrigerant is flown back to cool down superheated refrigerant on the suction side of the compressor so that operation in superheated condition of the compressor is securely prevented for further enhancing reliability of the compressor. When communication with the bypass passage is held for a set time once the expansion mechanism is opened, the compressor, can then be prevented in advance operation in wet condition due to frequent communication control of the main line. When the defrosting operation is completed, the open/shut-off means will be opened and the expansion mechanism is gradually opened. Since this ensures the minimum circulation amount of refrigerant at the shift to heating operation, heating performance can be increased. Since reverse flow of liquid refrigerant back to the compressor can be prevented, operation in wet condition of the compressor (1) can be prevented while dilution of lubricating oil in the compressor can be prevented. The present invention will now be described by reference to the drawings showing different embodiments. Fig. 1 is a block diagram showing the structure of the present invention. Fig. 2 is a refrigerant circuit diagram according to a first embodiment of the invention. Fig. 3 is a schematic diagram showing a receiver as used in this embodiment. Fig. 4 is a timing chart showing the control of defrosting operation. Fig. 5 is a refrigerant circuit diagram of a different second embodiment of the invention. Fig. 6 is a refrigerant circuit diagram of a third embodiment (not covered by the invention). Fig. 7 is a refrigerant circuit diagram of a fourth embodiment (not covered by the invention). Fig. 8 is a refrigerant circuit diagram showing another embodiment (also not covered by the invention). [BEST MODE FOR CARRYING OUT THE INVENTION] Below, embodiments of this invention will be described with reference to the drawings. - Embodiment 1 - Fig. 2 shows a refrigerant piping system of an air conditioner applying this invention, which is a so-called separate type one in which a single indoor unit (B) is connected to a single outdoor unit (A). The outdoor unit (A) comprises a compressor (1) of scroll type to be variably adjusted in operational frequency by an inverter, a four-way selector valve (2) switchable as shown in a solid line of Fig. 2 in cooling operation and in a broken line of Fig. 2 in heating operation, an outdoor heat exchanger (3) as a thermal-source-side heat exchanger which functions as a condenser in cooling operation and as an evaporator in heating operation, and a pressure reduction part (20) for reducing refrigerant in pressure. The outdoor heat exchanger (3) is provided with an outdoor fan (3f). In the indoor unit (B), there is disposed an indoor heat exchanger (6) as a used-side heat exchanger which functions as an evaporator in cooling operation and as a condenser in heating operation. The indoor heat exchanger (6) is provided with an indoor fan (6f). The compressor (1), the four-way selector valve (2), the outdoor heat exchanger (3), the pressure reduction part (20) and the indoor heat exchanger (6) are sequentially connected through refrigerant piping (8), thereby forming a refrigerant circuit (9) in which circulation of refrigerant causes heat transfer. The pressure reduction part (20) includes a bridge-like rectification circuit (8r) and a common passage (8a) connected to a pair of connection points (P, Q) of the rectification circuit (8r). In the common passage (8a), there are arranged in series a receiver (4), which is placed in an upstream-side common passage (8X) serving as a high-pressure liquid line at any time, for storing liquid refrigerant, an auxiliary heat exchanger (3a) for outdoor heat exchanger (3), and a motor-operated expansion valve (5) freely adjustable in opening, which serves as an expansion mechanism having a function of reducing liquid refrigerant in pressure and a function of adjusting a flow rate of liquid refrigerant. Another pair of connection points (R, S) of the rectification circuit (8r) are connected to the indoor heat exchanger (6) side of the refrigerant piping (8) and the outdoor heat exchanger (3) side of the refrigerant piping (8) respectively. There is formed a main line (9a) in which the compressor (1), the four-way selector valve (2), the outdoor heat exchanger (3), the rectification circuit (8r) and the common passage (8a) are sequentially connected and the rectification circuit (8r), the indoor heat exchanger (6), the four-way selector valve (2) and the compressor (1) are sequentially connected. Further, the rectification circuit (8r) is provided with: a first inflow passage (8b1) which connects the upstream-side connection point (P) of the common passage (8a) to the connection point (S) on the outdoor heat exchanger (3) side and has a first non-return valve (D1) for allowing refrigerant to flow only in a direction from the outdoor heat exchanger (3) to the receiver (4); a second inflow passage (8b2) which connects the upstream-side connection point (P) of the common passage (8a) to the connection point (R) on the indoor heat exchanger (6) side and has a second non-return valve (D2) for allowing refrigerant to flow only in a direction from the indoor heat exchanger (6) to the receiver (4); a first discharge passage (8c1) which connects the downstream-side connection point (Q) of the common passage (8a) to the connection point (R) on the indoor heat exchanger (6) side and has a third non-return valve (D3) for allowing refrigerant to flow only in a direction from the motor-operated expansion valve (5) to the indoor heat exchanger (6); and a second discharge passage (8c2) which connects the downstream-side connection point (Q) of the common passage (8a) to the connection point (S) on the outdoor heat exchanger (3) side and has a fourth non-return valve (D4) for allowing refrigerant to flow only in a direction from the motor-operated expansion valve (5) to the outdoor heat exchanger (3). Between both the connection points (P, Q) of the common passage (8a) of the rectification circuit (8r), a liquid seal preventing bypass passage (8f) provided with a capillary tube (C) is formed. The liquid seal preventing bypass passage (8f) prevents liquid seal at the deactivation of the compressor (1). Further, between the upper part of the receiver (4) and a part of the downstream-side common passage (8Y) which is located on a downstream side of the motor-operated expansion valve (5) and serves as a low-pressure liquid line at any time, there is provided an open/shut-off valve (SV) as open/shut-off means connected to a bypass passage (4a) for bypassing the motor-operated expansion valve (5), thereby venting gas refrigerant stored in the receiver (4). In detail, as shown in Fig. 3, the receiver (4) is connected at a body casing (41) thereof to the upstream-side common passage (8X), the downstream-side common passage (8Y) and the bypass passage (4a). The downstream-side common passage (8Y) is introduced into an inner bottom part of the body casing (41) in order that liquid refrigerant is discharged therefrom. The bypass passage (4a) is connected to the upper part of the body casing (41) in order that gas refrigerant is discharged therefrom. The degree of pressure reduction of the capillary tube (C) is set at a sufficiently larger value than the motor-operated expansion valve (5) so that the motor-operated expansion valve (5) adequately maintains the function of adjusting a flow rate of refrigerant in normal operation. (F1 to F4) indicate filters for removing dusts from refrigerant, and (ER) indicates a silencer for reducing operational sound of the compressor (1). The air conditioner is provided with various sensors. (Thd) is a discharge pipe sensor, which is disposed in a discharge pipe of the compressor (1), for sensing a discharge-pipe temperature Td as a refrigerant temperature on a discharge side of the compressor (1). (Tha) is an outdoor inlet sensor, which is disposed in an air inlet of the outdoor unit (A), for sensing an outdoor-air temperature Ta as an open-air temperature. (Thc) is an outdoor heat-exchange sensor, which is disposed in the outdoor heat exchanger (3), for sensing an outdoor heat-exchange temperature Tc as a condensation temperature in cooling operation and as an evaporation temperature in heating operation. (Thr) is an indoor inlet sensor, which is disposed in an air inlet of the indoor unit (B), for sensing an indoor-air temperature Tr as a room temperature. (The) is an indoor heat-exchange sensor, which is disposed in the indoor heat exchanger (6), for sensing an indoor heat-exchange temperature Te as an evaporation temperature in cooling operation and as a condensation temperature in heating operation. (HPS) is a high-pressure-control pressure switch for sensing a pressure of high-pressure refrigerant and turning on at the excessive rise in pressure of high-pressure refrigerant to output a high-pressure signal. (LPS) is a low-pressure-control pressure switch for sensing a pressure of low-pressure refrigerant and turning on at the excessive drop in pressure of low-pressure refrigerant to output a low-pressure signal. Respective output signals of the sensors (Thd to The) and the switches (HPS, LPS) are inputted into a controller (10). The controller (10) is so composed as to control air conditioning according to the input signals. In the above-mentioned refrigerant circuit (9), circulation of refrigerant in cooling operation is made in the following manner. Refrigerant is condensed in the outdoor heat exchanger (3) so as to be liquefied. Liquid refrigerant thus liquefied flows through the first non-return valve (D1) from the first inflow passage (8b1), is then stored in the receiver (4), is reduced in pressure by the motor-operated expansion valve (5), flows through the first discharge passage (8cl), and is evaporated in the indoor heat exchanger (6). Refrigerant thus evaporated returns to the compressor (1). On the other hand, circulation of refrigerant in heating operation is made in the following manner. Refrigerant is condensed in the indoor heat exchanger (6) so as to liquefied. Liquid refrigerant thus liquefied flows through the second non-return valve (D2) from the second inflow passage (8b2), is then stored in the receiver (4), is reduced in pressure by the motor-operated expansion valve (5), flows through the second discharge passage (8c2), and is evaporated in the outdoor heat exchanger (3). Refrigerant thus evaporated returns to the compressor (1). The controller (10) sections an operational frequency of the inverter into 20 steps N from zero to the maximum frequency, controls the capacity of the compressor (1) by finding out each frequency step N so that the discharge-pipe temperature Td becomes an optimum discharge-pipe temperature, and controls the opening of the motor-operated expansion valve (5) so that the discharge-pipe temperature Td becomes an optimum discharge-pipe temperature. The controller (10) has, as a feature of this invention, a defrosting executing means (11), an initial control means (12), a wet condition control means (13), a superheating control means (14) and an operation shifting means (15). The defrosting executing means (11) is so composed as to make the motor-operated expansion valve (5) fully closed and make the open/shut-off valve (SV) open according to a defrosting requiring signal outputted when the refrigerant circuit (9) becomes specified conditions and to execute defrosting operation in the reverse cycle. For example, the controller (10) memorizes the sum of heating performance from the start of heating operation after the end of defrosting operation, divides the sum of heating performance by the period of time that a heating operation period after the end of defrosting operation and a defrosting operation period to be preliminary expected are added to calculate a mean value of heating performance, and outputs a defrosting requiring signal when the mean value of heating performance is below the last-time mean value of heating performance. In any one of the case that the frequency step N of the compressor (1) drops to 6, the case that the discharge-pipe temperature Td rises above 110°C and the case that the defrosting operation period becomes longer than 10 minutes, the defrosting executing means (11) completes the defrosting operation. The initial control means (12) outputs an initially closing signal to the defrosting executing means (11), until a set time passes from the start of the defrosting operation, e.g., until 15 seconds pass, so as to make the open/shut-off valve (SV) closed, thereby closing the refrigerant circuit (9) for 15 seconds. The wet condition control means (13) outputs a closing signal for closing the open/shut-off valve (SV) to the defrosting executing means (11), so that when the discharge-pipe temperature Td of the compressor (1) drops below a specified temperature, e.g., 85°C, the open/shut-off valve (SV) holds a closed state for a set time and then becomes an opened state, e.g., for 20 seconds. Further, the wet condition control means (13) outputs an opening holding signal to the defrosting executing means (11) so that the open/shut-off valve (SV) holds for a set time the opened state after closed, e.g., so that the open/shut-off valve (SV) holds the opened state for 30 seconds by activating a timer for 50 seconds after the output of the closing signal. The superheating control means (14) outputs respective signals for opening and closing the motor-operated expansion valve (5) to the defrosting executing means (11), so that when the discharge-pipe temperature Td of the compressor (1) rises above a specified temperature, e.g., 90°C, the motoroperated expansion valve (5) is opened to a specified opening and then closed into a fully closed state. In other words, the superheating control means (14) once opens the motor-operated expansion valve (5) of a fully closed state to a partially opened state of 200 pulses, in which a fully opened state of the motor-operated expansion valve (5) is indicated as 480 pulses, and then fully closes it. Further, the super-heating control means (14) outputs a full-close holding signal to the defrosting executing means (11) so that the motor-operated expansion valve (5) holds for a set time a fully closed state after opened and closed. In detail, the superheating control means (14) activates the timer for one minute after the output of the opening and closing signals and prohibits the second and later times opening/closing operations until one minute passes. The operation shifting means (15) executes the shift from defrosting operation to heating cycle operation when the defrosting executing means (11) completes defrosting operation, so as to control the open/shut-off valve (SV) to hold it open for a set time in a heating cycle and then turn it closed while controlling the motor-operated expansion valve (5) to gradually open it to a specified opening. In detail, the operation shifting means (15) opens the open/shut-off valve (SV) for two minutes after the completion of defrosting operation and then closes it, while executing gradually opening control of the motor-operated expansion valve (5) for three minutes after the completion of defrosting operation in such a manner as to once open the motor-operated expansion valve (5) of a fully closed state to 80 pulses, hold it in the partially opened state for 10 seconds, and then open it by 2 pulses in every five seconds or open it by 1 pulse in every 10 seconds when the outdoor-air temperature Ta is 23°C or less. - Defrosting operation in Embodiment 1 - Next, description will be made about controls of defrosting operation of the air conditioner above-mentioned, with reference to a timing chart of Fig. 4. First, in heating cycle operation, the four-way selector valve (2) is turned to an ON state as shown from a point a to point b, that is, switched to the broken line shown in Fig. 2, to fuzzy-control the opening of the motor-operated expansion valve (5) and the frequency step N of the compressor (1) so as to be an optimum discharge-pipe temperature, thereby performing heating operation. At the point b, the controller (10) outputs a defrosting requiring signal according to a mean value of heating performance. When the defrosting requiring signal is outputted, defrosting operation waits until preparation of defrosting operation in the indoor unit (B) is completed at a point c, e.g., until treatment on a heater or the like is completed, the low-pressure-control pressure switch (LPS) is masked and then defrosting operation further waits for 35 seconds to a point d, i.e., to the time that the frequency step N of the compressor (1) to switch the four-way selector valve (2), which is 6, comes. Thereafter, from the point d, fully closing operation for making the opening of the motor-operated expansion valve (5) into 0 pulse is started and liquid refrigerant stored in the outdoor heat exchanger (3) is recovered. When the time sufficient for fully closing the motor-operated expansion valve (5) has passed, the indoor fan (6f) is deactivated at a point e and heat storage in the indoor heat exchanger (6) is executed with high-pressure refrigerant. This heat storage operation is completed when it has been executed for at most 10 seconds, when the indoor heat-exchange temperature Te rises above 35°C, when the outdoor heat-exchange temperature Tc drops below -30°C, or when the present outdoor heat-exchange temperature Tc drops 4°C more than the outdoor heat-exchange temperature Tc at the time before the heat storage is started (See a point f). At this point f, the defrosting executing means (11) deactivates the outdoor fan (3f), switches the four-way selector valve (2), i.e., switches according to the defrosting requiring signal the four-way selector valve (2) as shown in the solid line of Fig. 2 to set it to a cooling cycle, and feeds to the outdoor heat exchanger (3) high-temperature refrigerant discharged from the compressor (1) to start defrosting operation in the reverse cycle. As a feature of this invention, when the defrosting operation is started, the defrosting executing means (11) ordinarily closes the motor-operated expansion valve (5) into a fully closed state of 0 pulse and opens the open/shut-off valve (SV), thereby shutting off the common passage (8a) and opening the bypass passage (4a). However, since the initial control means (12) outputs an initially closing signal, the open/shut-off valve (SV) is closed so that the common passage (8a) and the bypass passage (4a) are shut off until 15 seconds passes. In detail, switching of the four-way selector valve (2) reverses the pressure distribution of refrigerant in the refrigerant circuit (9) to make the refrigerant pressure in the receiver (4) higher than the respective refrigerant pressures in the outdoor heat exchanger (3) and the indoor heat exchanger (6). If under such conditions the motor-operated expansion valve (5) and the open/shut-off valve (SV) remain opened, liquid refrigerant of high-temperature and high-pressure flows through the outdoor heat exchanger (3) and the indoor heat exchanger (6). Further, in such a case, liquid refrigerant is evaporated in the indoor heat exchanger (6), and refrigerant thus evaporated expels liquid refrigerant from the indoor heat exchanger (6) so that liquid refrigerant excessively flows into the compressor (1), while liquid refrigerant flowing into the outdoor heat exchanger (3) reduces a condensation area. As a result, defrosting performance is reduced. To solve this problem, as mentioned above, the motor-operated expansion valve (5) and the open/shut-off valve (SV) are closed thereby preventing the discharge of liquid refrigerant from the receiver (4). Thereafter, when 15 seconds have passed, the defrosting executing means (11) opens the open/shut-off valve (SV) at a point g to execute ordinary defrosting operation and gradually increases the operational frequency N of the compressor (1). Then, refrigerant discharged from the compressor (1) is condensed in the outdoor heat exchanger (3) to dissolve frost and flows into the receiver (4). From the receiver (4), gas refrigerant flows into the indoor heat exchanger (6) via the bypass passage (4a) and returns to the compressor (1). By such circulation of refrigerant, defrosting operation is executed. Subsequently, when the discharge-pipe temperature Td rises above 90 °C in the defrosting operation, between a point h and a point i the superheating control means (14) outputs respective signals for opening and closing the motor-operated expansion valve (5) to once open the motor-operated expansion valve (5) to 200 pulses and then close it. In detail, gas refrigerant is discharged from the receiver (4) and flows through the bypass passage (4a). However, in the case of defrosting at a high open-air temperature or the case of long refrigerant piping, it readily becomes short of refrigerant so that the compressor (1) causes operation in superheated condition thereby increasing the discharge-pipe temperature Td. To cope with this problem, the superheating control means (14) once opens the motor-operated expansion valve (5) to introduce liquid refrigerant in the receiver (4) into the indoor heat exchanger (6) through the downstream-side common passage (8Y) as shown in Fig. 3, thereby preventing the operation in superheated condition. The opening/closing operation of the motor-operated expansion valve (5) is executed a single time in every one minute. In detail, as shown in a term j, after outputting an opening signal and a closing signal, the superheating control means (14) outputs a full-close holding signal so that the motor-operated expansion valve (5) holds for one minute the fully closed state after opened and closed, thereby prohibiting the excessive opening/closing operation. On the other hand, when the discharge-pipe temperature Td drops below 85°C in the defrosting operation, between a point k and a point l the wet condition control means (13) outputs a closing signal for the open/shut-off valve (SV) to hold the open/shut-off valve (SV) closed for 20 seconds. In detail, gas refrigerant is discharged from the receiver (4) and flows through the bypass passage (4a). However, if the receiver (4) is filled with liquid refrigerant, liquid refrigerant turns back to the compressor (1) through the indoor heat exchanger (6) so that the compressor (1) operates in wet condition, thereby decreasing the discharge-pipe temperature Td. To cope with this problem, the wet condition control means (13) closes the open/shut-off valve (SV) and shuts off the common passage (8a) and the bypass passage (4a) to prevent liquid refrigerant from turning back, thereby preventing the operation in wet condition. The closing operation of the open/shut-off valve (SV) is executed a single time in every 50 seconds. In detail, as shown in a term m, after outputting a closing signal, the wet condition control means (13) outputs an opening holding signal so that the open/shut-off valve (SV) holds for 50 seconds the opened state after closed, thereby prohibiting the excessive closing operation. Thereafter, in any one of the case that the frequency step N of the compressor (1) drops to 6, the case that the discharge-pipe temperature Td rises above 110°C, and the case that the defrosting operation period becomes longer than 10 minutes, as shown in a point n, the defrosting executing means (11) completes defrosting operation, turns the four-way selector valve (2) to an ON state to switch it as shown in the broken line of Fig. 2 and activates the outdoor fan (3f), thereby starting heating operation in a hot start. At the time just before the defrosting operation is completed, the frequency step N of the compressor (1) is set to become 6 without exception according to the timer or the discharge-pipe temperature Td. Then, when the defrosting operation is completed, between a point n and a point o the operation shifting means (15) opens the open/shut-off valve (SV) for 2 minutes and then closes it to prevent the short of refrigerant, while between the point n and a point p the operation shifting means (15) gradually opens the motor-operated expansion valve (5) to prevent the operation in wet condition. In detail, the operation shifting means (15) first opens the motor-operated expansion valve (5) in a partially opened state of 80 pulse, holds it in this state for 10 seconds, then opens the motor-operated expansion valve (5) by 2 pulses in every 5 seconds or opens it by 1 pulse in every 10 seconds in the case of the outdoor-air temperature Ta of 23°C or less, and fuzzy-controls the opening of the motor-operated expansion valve (5) and the frequency step N of the compressor (1) so as to become the optimum discharge-pipe temperature, thereby restarting normal heating operation. - Characteristic Effects of Embodiment 1 - According to the present embodiment, since the open/shut-off valve (SV) is opened in defrosting operation so that gas refrigerant in the receiver (4) is introduced into the main line (9a) via the bypass passage (4a), when liquid refrigerant condensed in the outdoor heat exchanger (3) is stored in the receiver (4) in the case of heavy frost, low open-air temperature or short refrigerant piping, liquid refrigerant in the receiver (4) can be securely prevented from turning back to the compressor (1) without provision of any accumulator. As a result, operation in wet condition of the compressor (1) can be securely prevented so that the compressor (1) is subjected to no stress, thereby enhancing reliability of the compressor (1). Further, since no accumulator is needed, pressure loss can be decreased thereby enhancing operation performance, and the number of elements can be reduced thereby resulting in cost reduction. Furthermore, since the motor-operated expansion valve (5) and the open/shut-off valve (SV) are closed at the initial stage of the defrosting operation, it can be securely prevented that liquid refrigerant in the receiver (4) flows into the outdoor heat exchanger (3) and the indoor heat exchanger (6) due to variation in pressure of the refrigerant circuit caused by switching the four-way selector valve (2). Thus, turning back of liquid refrigerant to the compressor (1) can be prevented and a condensation area in the outdoor heat exchanger (3) can be sufficiently ensured, so that defrosting performance can be increased. Further, since the open/shut-off valve (SV) is closed when the discharge-pipe temperature Td drops in the defrosting operation, liquid refrigerant on a suction side of the compressor (1) can be evaporated. Consequently, turning back of liquid refrigerant can be prevented so that operation in wet condition of the compressor (1) can be securely prevented, thereby further enhancing reliability of the compressor (1). Furthermore, since the open/shut-off valve (SV) once closed is held in an opened state for a set time, the compressor (1) can be prevented in advance from operating in superheated condition due to frequent closing control of the open/shut-off valve (SV). Further, since the motor-operated expansion valve (5) is opened when the discharge-pipe temperature Td rises in the defrosting operation, liquid refrigerant is turned back to cool down superheated refrigerant on a suction side of the compressor (1), so that operation in superheated condition of the compressor (1) can be securely prevented thereby further enhancing reliability of the compressor (1). Furthermore, since the motor-operated expansion valve (5) is once opened and is then held in a fully closed state for a set time, the compressor (1) can be prevented in advance from operating in wet condition due to frequent opening/closing control of the motor-operated expansion valve (5). In other words, the wet condition control means (13) and the superheating control means (14) hold the discharge-pipe temperature Td in an optimum temperature so that the compressor (1) is subjected to no stress. Moreover, when the defrosting operation is completed, the open/shut-off valve (SV) is opened and the motor-operated expansion valve (5) is gradually opened. Since this ensures the minimum circulation amount of refrigerant at the shift to heating operation, heating performance can be increased. Further, since turning back of liquid refrigerant to the compressor (1) can be prevented, operation in wet condition of the compressor (1) can be prevented while dilution of lubricating oil in the compressor (1) can be prevented. - Modification of Embodiment 1 - Fig. 5 shows a motor-operated valve (V1) freely adjustable in opening, which is substituted for the open/shut-off valve (SV) of the above embodiment. Said valve (V1) is an open/shut-off means in the sense of claim 1. Other structure, operations and effects are the same as in the above embodiment. The opening of the motor-operated valve (V1) may be controlled into a fully opened state and a fully closed state, or may be otherwise adjusted according to the discharge-pipe temperature Td or the like. - Embodiment 2 - Fig. 6 shows an embodiment which is not covered by the claims. In the present embodiment, a three way valve (V2) is substituted for the open/shut-off valve (SV) of the above embodiment, and the bypass passage (4a) is connected to a high-pressure side of the motor-operated expansion valve (5). The three way valve (V2) forms a selector means switchable between a bypass communication state in which the high-pressure side of the motor-operated expansion valve (5) is communicated with the bypass passage (4a) and a main line communication state in which the high-pressure side of the motor-operated expansion valve (5) is communicated with the common passage (8a) of the main line (9a). - Structure and Operation of Defrosting Operation Control of Embodiment 2 - Description will be made about the structure and operations of defrosting operation control in an embodiment of Fig. 6, with reference to the timing chart of Fig. 4. First, when the defrosting executing means (11A1) starts defrosting operation at a point f, it switches the four-way selector valve (2) as shown in the solid line of Fig. 6 and switches the three way valve (V2) as shown in the broken line of Fig. 6, so that the bypass passage (4a) is communicated with the motor-operated expansion valve (5) thereby resulting in the bypass communication state. Further, the initial control means (12A1) controls the motor-operated expansion valve (5) to hold it in a fully closed state for 15 seconds in correspondence with the closure of the open/shut-off valve (SV) in the before-mentioned embodiment (See points f to g of Fig. 4). Thereafter, the motor-operated expansion valve (5) is opened at a specified opening and is held in the specified opening, so that gas refrigerant in the receiver (4) is introduced toward the indoor heat exchanger (6) through the bypass passage (4a) thereby executing defrosting operation. When the discharge-pipe temperature Td rises above 90 °C in the defrosting operation, the superheating control means (14A1) outputs a switching signal to switch the three way valve (V2) as shown in the solid line of Fig. 6 thereby forming the main line communication state. Then, the super-heating control means (14A1) switches again the three way valve (V2) as shown in the broken line of Fig. 6 thereby forming the bypass communication state, and subsequently outputs a switching holding signal to hold the bypass communication state for a set time (See points h to i and a term j of Fig. 4). In other words, because the compressor (1) is on its way to superheated condition, operation in superheated condition is prevented by the introduction of liquid refrigerant in the receiver (4) toward the indoor heat exchanger (6). On the other hand, when the discharge-pipe temperature Td drops below 85°C, the wet condition control means (13A1) outputs a fully closing signal to make the motor-operated expansion valve (5) fully closed for 20 seconds, and subsequently outputs a full-close holding signal to hold the motor-operated expansion valve (5) in a specified opened state for 30 seconds (See points k to l and a term m of Fig. 4). In other words, because the compressor (1) is on its way to wet condition, the common passage (8a) and the bypass passage (4a) are shut off together thereby preventing the operation in wet condition. Thereafter, when the defrosting operation is completed (See a point n of Fig. 4), the four-way selector valve (2) is switched as shown in the broken line of Fig. 6 and the three way valve (V2) is switched as shown in the solid line of Fig. 6 so that the main line communication state is formed, while the motor-operated expansion valve (5) is opened to a target opening. Thus, normal heating operation is restarted. Other structure and operations are the same as in the before-mentioned embodiment. Accordingly, in the present embodiment, similar to the before-mentioned embodiment, operation in wet condition and operation in superheated condition of the compressor (1) can be securely prevented without any accumulator, thereby enhancing operation performance and reliability of the compressor (1). - Embodiment 3 - Fig. 7 shows another embodiment which is not covered by the claims. In the present embodiment, the bypass passage (4a) is connected to a low-pressure side of the motor-operated expansion valve (5) instead of being connected to the high-pressure side of the motor-operated expansion valve (5) in the above embodiment of Fig. 6. The three way valve (V2) forms a selector means switchable between a bypass communication state in which the downstream-side common passage (8Y) is communicated with the bypass passage (4a) and a main line communication state in which the downstream-side common passage (8Y) is communicated with the common passage (8a). - Structure and Operation of Defrosting Operation Controls of Embodiment 3 - Description will be made about the structure and operations of defrosting operation control in an embodiment of Fig. 7, with reference to the timing chart of Fig. 4. First, when the defrosting executing means (11A2) starts defrosting operation at a point f, it switches the four-way selector valve (2) as shown in the solid line of Fig. 7 and switches the three way valve (V2) as shown in the broken line of Fig. 7, so that the bypass passage (4a) the bypass passage (4a) is communicated with the downstream-side common passage (8Y), thereby resulting in the bypass communication state. Further, the initial control means (12A2) holds the three way valve (V2) in the main line communication state shown in the solid line of Fig. 7 while controlling the motor-operated expansion valve (5) to hold it in a fully closed state for 15 seconds in correspondence with the closure of the open/shut-off valve (SV) in the before-mentioned embodiment (See points f to g of Fig. 4). Thereafter, the defrosting executing means (11A2) switches the three way valve (V2) as shown in the broken line of Fig. 7 to form the bypass communication state, so that gas refrigerant in the receiver (4) is introduced toward the indoor heat exchanger (6) through the bypass passage (4a) thereby executing defrosting operation. When the discharge-pipe temperature Td rises above 90°C in the defrosting operation, the superheating control means (14A2) outputs a switching signal to switch the three way valve (V2) as shown in the solid line of Fig. 7 thereby forming the main line communication state, and opens the motor-operated expansion valve (5) to a specified opening. Then, the superheating control means (14A2) switches again the three way valve (V2) as shown in the broken line of Fig. 7 thereby forming the bypass communication state, and subsequently outputs a switching holding signal to hold the bypass communication state for a set time (See points h to i and a term j of Fig. 4). In other words, because the compressor (1) is on its way to superheated condition, operation in superheated condition is prevented by the introduction of liquid refrigerant in the receiver (4) toward the indoor heat exchanger (6). On the other hand, when the discharge-pipe temperature Td drops below 85°C, the wet condition control means (13A2) outputs a switching signal to switch the three way valve (V2) as shown in the solid line of Fig. 7 thereby forming the main line communication state, and makes the motor-operated expansion valve (5) fully closed for 20 seconds. Then, the wet condition control means (13A2) switches again the three way valve (V2) as shown in the broken line of Fig. 7 thereby forming the bypass communication state, and subsequently outputs a switching holding signal to hold the bypass communication state for a set time (See points k to l and a term m of Fig. 4). In other words, because the compressor (1) is on its way to wet condition, the common passage (8a) and the bypass passage (4a) are shut off together thereby preventing the operation in wet condition. Thereafter, when the defrosting operation is completed (See a point n of Fig. 4), the four-way selector valve (2) is switched as shown in the broken line of Fig. 7 and the three way valve (V2) is switched as shown in the solid line of Fig. 7 so that the main line communication state is formed, while the motor-operated expansion valve (5) is opened to a target opening. Thus, normal heating operation is restarted. Other structure and operations are the same as in the before-mentioned embodiment of Fig. 2. Accordingly, in the present embodiment, similar to the before-mentioned embodiment, operation in wet condition and operation in superheated condition of the compressor (1) can be securely prevented, thereby enhancing reliability of the compressor (1). - Embodiment 4 - Fig. 8 shows another embodiment which is not covered by the claims. In the present embodiment, a capillary (CP) is provided instead of the open/shut-off valve (SV) of the embodiment of Fig. 2. Accordingly, in defrosting operation, the motor-operated expansion valve (5) is fully closed so that gas refrigerant in the receiver (4) flows through the bypass passage (4a). - Other Modifications - In the above embodiments, operation control of the compressor (1) in wet condition and in superheated condition in defrosting operation is executed in such a manner that the open/shut-off valve (SV), the motor-operated expansion valve (5) and the like are opened and closed. In the invention according to claim 1, however, the bypass passage (4a) may be communicated at any time during defrosting operation. Further, in the invention according to claims 3 and 5, the compressor (1) may be controlled based on a pressure of refrigerant on the discharge side. Furthermore, the refrigerant circuit (9) is not limited to the above embodiments. For example, it may be a refrigerant circuit having no rectification circuit (8r). [INDUSTRIAL APPLICABILITY] As described so far, this invention is useful for air conditioners having no accumulator.

Claims: An air conditioner comprising a refrigerant circuit (9) which by means of an operation control device (10) is reversibly operable between a cooling cycle operation and a heating cycle operation and in which a compressor (1), a thermal-source-side heat exchanger (3), an expansion mechanism (5) freely adjustable in opening and a used-side heat exchanger (6) are sequentially connected along a main line (9a) of the refrigerant circuit (9), a receiver (4) for storing liquid refrigerant being arranged in a high-pressure liquid line of the refrigerant circuit (9), characterized by a bypass passage (4a) for bypassing the expansion mechanism (5) to introduce gas refrigerant from the receiver (4) into a low-pressure liquid line of the main line (9a) of the refrigerant circuit (9) downstream of the expansion mechanism (5), said bypass passage (4a) being connected at one end thereof to the receiver (4) and at the other end to said low-pressure liquid line, the receiver (4) being provided in a high-pressure liquid line of the main line (9a) of the refrigerant circuit (9); open/shut-off means (SV) provided in the bypass passage (4a) for opening and shutting off the bypass passage (4a); and defrosting executing means (11) for fully closing the expansion mechanism (5) and opening the open/shut-off means (SV) in response to a defrosting requiring signal in the heating cycle operation and for executing a defrosting operation in the cooling cycle of the refrigerant circuit (9). The air conditioner according to claim 1, characterized by initial control means (12) for outputting an initially closing signal to the defrosting executing means (11) for fully closing the open/shut-off means (SV) until a set time has passed after the start of the defrosting operation. The air conditioner according to claim 1 or 2, characterized by wet condition control means (13) for outputting a closing signal to the defrosting executing means (11) for fully closing the open/shut-off means (SV) when refrigerant temperature on the discharge side of the compressor (1) drops to or below a specified temperature. The air conditioner according to claim 3, characterized in that the wet condition control means (13) outputs an opening holding signal to the defrosting executing means (11) for holding the opened state of the open/shut-off means (SV) for a set time after the open/shut-off means (SV) has been fully closed for a set time. The air conditioner according to any of the claims 1 to 4, characterized by superheating control means (14) for outputting opening and closing signals to the defrosting executing means (11) so that when refrigerant temperature on the discharge side of the compressor (1) rises to or above a specified temperature the expansion mechanism (5) is first opened to a specified opening state and then fully closed. The air conditioner according to claim 5, characterized in that the superheating control means (14) outputs a closing holding signal to the defrosting executing means (11) for holding the fully closed state of the expansion mechanism (5) after the expansion mechanism (5) has been opened. The air conditioner according to any of the claims 1 to 6, characterized by operation shifting means (15) for shifting the refrigerant circuit (9) to the heating cycle operation after the defrosting executing means (11) has completed defrosting for holding the open/shut-off means (SV) opened for a set time in the heating cycle operation of the refrigerant circuit (9) and then closing the open/shut-off means (SV) while gradually opening the expansion mechanism (5) to a specified opening state.

Inventors: INOUE SEIKI, NAKAJIMA HIROTO, SAKAI SEIJI, INOUE, SEIKI, NAKAJIMA, HIROTO, SAKAI, SEIJI, INOUE, Seiki, Daikin Industries, Ltd., NAKAJIMA, Hiroto, Daikin Industries, Ltd., SAKAI, Seiji, Daikin Industries, Ltd.
Applicants: DAIKIN IND LTD, DAIKIN INDUSTRIES, LIMITED
Application year: 1994
Main classification: F25B47
IPC codes: F25B41, F25D21, F24F11, F25B47